I hope the OP has resolved the issue as best as possible by now, but for anyone else who may find this question: I haven't recreated this exact scenario, but I have had experiences of relationship attributes unexpectedly turning out as null, despite an apparently successful creation call. It was only after taking the time to create a minimal example scenario, all ready for a bug report, that I recalled this one, crucial line from the API documentation for Relationships:   RelationshipDefs can have AttributeDefs - though only primitive types are allowed. [emphasis mine] Given that the main Types documentation defines primitive types as " boolean, byte, short, int, long, float, double, biginteger, bigdecimal, string, date", I believe this is a plausible reason why setting the attribute as an array of map of type does not work: it is not a primitive type. Unfortunately, I've found the surfacing of errors in Atlas to be pretty inconsistent. A lot depends on the client library you're using; often a raw curl will give you a more detailed error message, but sometimes even that is not enough, and you'll need to consult the logs directly. In this case for example, it may have saved both of us a lot of time if there was just a higher-level check which detects trying to use non-primitive types in relationship attributes! ... View more

Hopefully the OP is sorted out by now, but for anyone else who comes across this: one of the best step-by-step instructions on Atlas relationships I've found is this comment by Vinayak Marriaya on the Atlas Jira; re-producing here, in case that link dies:   Following are the json's to create relationships 1. Creating EntityDef json 2. Creating Entity json 3. Creating RelationshipDef json 4. Creating Relationship instance json Step-1 Creating EntityDef POST -   http://localhost:21000/api/atlas/v2/types/typedefs   { "entityDefs" : [ { "category" : "ENTITY" , "name" : "type_a" }, { "category" : "ENTITY" , "name" : "type_b" } ] }   Step-2 Creating Entity POST -   http://localhost:21000/api/atlas/v2/entity/bulk   { "entities" : [ { "typeName" : "type_a" , "guid" : "-72ddefefS2UY" }, { "typeName" : "type_b" , "guid" : "-JL1HddDOfdf" } ] }   Step-3 Creating RelationshipDef POST -   http://localhost:21000/api/atlas/v2/types/typedefs   { "relationshipDefs" : [ { "propagateTags" : "ONE_TO_TWO" , "description" : "description ASSOCIATION between type5 and type6" , "relationshipCategory" : "ASSOCIATION" , "typeVersion" : "1.0" , "attributeDefs" : [ { "name" : "LinkInformation" , "typeName" : "string" , "isOptional" : true , "cardinality" : "SINGLE" , "valuesMinCount" : 0, "valuesMaxCount" : 1, "isUnique" : false , "isIndexable" : false , "includeInNotification" : false , "searchWeight" : -1 } ], "endDef2" : { "name" : "type_b_rel_attribute" , "isLegacyAttribute" : false , "isContainer" : false , "cardinality" : "SINGLE" , "type" : "type_b" , "description" : "description with name: type_2_rel_attribute" }, "endDef1" : { "name" : "type_a_rel_attribute" , "isLegacyAttribute" : false , "isContainer" : false , "cardinality" : "SET" , "type" : "type_a" , "description" : "description with name: type_1_rel_attribute" }, "guid" : "-2fsdfjhsewl04" , "name" : "association_type_a_and_type_b" } ] }   Step-4 Creating Relationship instance POST-   http://localhost:21000/api/atlas/v2/relationship   { "typeName" : "association_type_a_and_type_b" , "end1" : { "typeName" : "type_a" , "guid" : "b4dae5e8-a606-4e41-9ce3-8f35245f389e" (guid of type_a entity) }, "propagateTags" : "NONE" , "provenanceType" : 0, "propagatedClassifications" : [], "end2" : { "typeName" : "type_b" , "guid" : "23c2f3c1-dd74-4190-a6d1-b012c44cbb6d" (guid of type_b entity) }, "blockedPropagatedClassifications" : [], "guid" : "-bjbfdfddfeffef" , "attributes" : { "LinkInformation" : "TestingInformation" } }     Following is the output of the above API call. Output of type_a entity GET -   http://localhost:21000/api/atlas/v2/entity/guid/\{guid of type_a entity}   { "referredEntities" : {}, "entity" : { "typeName" : "type_a" , "guid" : "b4dae5e8-a606-4e41-9ce3-8f35245f389e" , "isIncomplete" : false , "status" : "ACTIVE" , "createdBy" : "admin" , "updatedBy" : "admin" , "createTime" : 1632121151626, "updateTime" : 1632121151626, "version" : 0, "relationshipAttributes" : { "type_a_rel_attribute" : [ { "guid" : "23c2f3c1-dd74-4190-a6d1-b012c44cbb6d" , "typeName" : "type_b" , "entityStatus" : "ACTIVE" , "relationshipType" : "association_type_a_and_type_b" , "relationshipGuid" : "ec64783a-58d7-4265-87d6-c1535ce2d9b7" , "relationshipStatus" : "ACTIVE" , "relationshipAttributes" : { "typeName" : "association_type_a_and_type_b" , "attributes" : { "LinkInformation" : "TestingInformation" } } } ] }, "labels" : [] } }   Output of type_b entity GET -   http://localhost:21000/api/atlas/v2/entity/guid/\{guid of type_b entity} { "referredEntities" : {}, "entity" : { "typeName" : "type_b" , "guid" : "23c2f3c1-dd74-4190-a6d1-b012c44cbb6d" , "isIncomplete" : false , "status" : "ACTIVE" , "createdBy" : "admin" , "updatedBy" : "admin" , "createTime" : 1632121151626, "updateTime" : 1632121151626, "version" : 0, "relationshipAttributes" : { "type_b_rel_attribute" : { "guid" : "b4dae5e8-a606-4e41-9ce3-8f35245f389e" , "typeName" : "type_a" , "entityStatus" : "ACTIVE" , "relationshipType" : "association_type_a_and_type_b" , "relationshipGuid" : "ec64783a-58d7-4265-87d6-c1535ce2d9b7" , "relationshipStatus" : "ACTIVE" , "relationshipAttributes" : { "typeName" : "association_type_a_and_type_b" , "attributes" : { "LinkInformation" : "TestingInformation" } } } }, "labels" : [] } } As you can see, LinkInformation is specified under "attributes" and when you search for the entity using GUID as you mentioned in jira, you will be able to see the value of "LinkInformation".   ... View more