The request was rejected because the total packed size of the session policies and session tags combined was too large. An Amazon Web Services conversion compresses the session policy document, session policy ARNs, and session tags into a packed binary format that has a separate limit. The error message indicates by percentage how close the policies and tags are to the upper size limit. For more information, see Passing Session Tags in STS in the IAM User Guide.
You could receive this error even though you meet other defined session policy and session tag limits. For more information, see IAM and STS Entity Character Limits in the IAM User Guide.