The Marketplace did it wrong.  They are supposed to only enter the last 15 characters.  So if there is more than 15, only enter the last 15.

Line 2.

Enter the number the Marketplace assigned to the policy. If the policy number is greater than 15 characters, enter only the last 15 characters.

https://www.irs.gov/instructions/i1095a#idm140607241930608