> The plan is to permanently affix a thicker piece of paper somewhere on the letter with regular glue, and then use “gummy glue” to temporarily attach the microSD card on top of it.
I'm with the person you're responding to. It's not clear from this description what he's doing, but it sounds like he's gluing paper to something (the envelop itself?) and then using gummy glue to attach the card to the thicker piece of paper. Credit cards just come attached to a piece of paper that is not, itself, attached to anything else. It's not obvious to me why he'd do it this way.
I'm with the person you're responding to. It's not clear from this description what he's doing, but it sounds like he's gluing paper to something (the envelop itself?) and then using gummy glue to attach the card to the thicker piece of paper. Credit cards just come attached to a piece of paper that is not, itself, attached to anything else. It's not obvious to me why he'd do it this way.