Error 'Field is not writeable: OpportunityTeamMember.OpportunityAccessLevel' on API insert of OpportunityTeamMember

Solution: Omit the OpportunityAccessLevel Field:

OpportunityTeamMember records can still be created via API even when Org Wide Defaults are set to Private for Opportunities. The solution is to omit the OpportunityAccessLevel field from the Apex insert statement entirely.

Example: Successful Insert (Without OpportunityAccessLevel)

For example this code successfully creates a new Opportunity Team Member via API:

insert new opportunityteammember(OpportunityId='006000000000000AAD', TeamMemberRole='Account Manager', UserId='00500000000000OAA2');

Example: Failing Insert (With OpportunityAccessLevel)

This code returns the error because OpportunityAccessLevel is included in the apex insert statement.

insert new opportunityteammember(OpportunityAccessLevel='Edit', OpportunityId='006000000000000AAD', TeamMemberRole='Account Manager', UserId='00500000000000OAA2');