How do I change photo's allowed from 12 to 24 for a single ad?

[coastaltechsolution]

You get 12 but if you add more you get charged?

[southern*sweet*tea]

You only have twelve, unless you have a variations listing of some sort. Those can have more.

[dhbookds]

You only get 12 in the top left box...... and can't pay for more anymore I don't think.

I think you can still embed extra pictures in the description......using HTML....but I've never done it......you might ask over on the Tools board. 

That said, one reason to not overload a listing used to be the time it took to load on a phone.....that might still be a consideration.......

[reallynicestamps]

I've added pictures in my description with the pictures being hosted off-eBay.

But the Gallery is limited to 12, which are free.  I suspect eBay doesn't have the server space to host more.

[chapeau-noir]

Whatever photo hosting service you use needs to be encrypted, though, and having loads of photos in a description really drags it out.

An alternative is using collages.

[coolections]

Unless you have a million items in your ad I see no reason for 24 photos. Buyers would get bored real fast.

[jayjaspersgarage]

There is nothing you offer for sale that requires more than twelve photos.  Perhaps if you are going to list a vehicle more than a dozen photos would be warranted.

[bimm_corp]

You could try like I do here,

https://www.ebay.com/itm/284221913124

pasting two photos together, then uploading it as one pic. I use MS Paint to cobble them together, but there are probably programs that will do a nicer and more professional job. HTH.