I did a quick search and didn't find a similar issue, but I apologize if I missed one on this topic. And, maybe this is an enhancement request rather than a bug report. It is an inconsistency in type names between the url and rendered document.

For an api view of a model I have eg http://localhost/api/customer-accounts/ where the relationship type (lets just call it relationship-name) is inflected correctly according to the setting JSON_API_FORMAT_TYPES (dasherized, in this case)

{
 "links": {
 "first": "http://localhost/api/customer-accounts/?page%5Bnumber%5D=1",
 "last": "http://localhost/api/customer-accounts/?page%5Bnumber%5D=1",
 "next": null,
 "prev": null
 },
 "data": [
 {
 "type": "customer-accounts",
 "id": "1",
 "attributes": {
 "account-id": 1,
 "account": "1234",
 "insert-ts": "2020年05月20日T20:42:52.895506Z",
 "update-ts": "2020年05月20日T20:42:52.895643Z"
 },
 "relationships": {
 "relationship-name": {
 "data": {
 "type": "relationship-name",
 "id": "1"
 }
 }
 }
 }
 ],
 "meta": {
 "pagination": {
 "page": 1,
 "pages": 1,
 "count": 1
 }
 }
}

Then I go to eg http://localhost/api/customer-accounts/1/relationships/relationship-name/ and get a 404. Instead, I find the relationship at http://localhost/api/customer-accounts/1/relationships/relationship_name/ which looks like:

{
 "data": {
 "type": "relationship-name",
 "id": "1"
 }
}

The rendered document has the correctly inflected type, which doesn't match the url.

I am working around this for now using field name mapping in RelationshipView

field_name_mapping = {
 'relationship-name': 'relationship_name'
 }

Could RelationshipView pass relationship-name through the inflector first to get it back to the internal python (underscore) convention?