Standard Envelope option greyed out

[wolfsvintagepostcards]

I use standard envelope to ship all my postcards under $20.00. Have sent many many postcards out no problem. Someone bought this item last night https://www.ebay.com/itm/124943216485 . I use the exact same template I use for all my single postcards. Somehow the standard envelope option is greyed out?! Makes no sense to me.  4 other sales today had no problem printing the standard envelope. Need it to keep top-rated status.

[disneyshopper]

Make sure the thickness is listed as   0  inches.

[wolfsvintagepostcards]

Tried that didn't change it from greyed out. Contacted ebay and they sent it to IT. They gave me the difference & I upped it to first class.