Wedding attire

I don't know if this is going to work exactly for vests or if it'll look nice but some people for pants for the button, will use a rubber band to extend it. Basically they just hook the rubber band around the button.

That’s exactly what I was thinking, I just didn’t know if it would work for vests, thank you for your help. I said I’d see if they have a size bigger, but it’s really close now, and he said if I can’t get another we’ll make it work

You may be able to move the buttons over a little bit closer to the finished edge of the vest front. That won't likely give him a lot of extra room, but it might be enough for him to breathe. Beyond that if you or a seamstress can tell how much seam allowance there is in the side seams, it might be worth taking it completely apart to let it out. However, if there's not much seam allowance, that is probably more work than it's worth unless you can find fabric that is close enough and add panels along the side seams to make it bigger. If nothing else, just let him wear it unbuttoned.

If it is only for a few minutes and there is no way to get another size, another option is to reinforce the buttons. It won't be as comfy as loosening it (can you move the buttons over to allow more room?) but if you can't officially make alterations to the vest this might at least prevent wardrobe malfunctions for the duration of the ceremony

I ordered another, but if it doesn’t match, he’ll just have to suck it in for 15 minutes or so, lol