If you were able to restore wallet using the same seed phrase you had written down originally without any problems, the case shouldn’t be any different even after funding with a good sum.
My best guess is, you have done something to the wallet in your derivation part.
It’s always a garbage in and garbage out for these systems.
How about you don’t try to be any sophisticated and just try to restore a standard wallet, following numeral procedures. You shouldn’t have any problems restoring your wallet address.
I don't know if this can help, since you mentioned iancoleman and it's showing invalid please watch out for capital letters in your seed phrase, they should all be in small letters especially the first word.
Another one is space, I know it can sound stupid but I once found myself in this same position, normally as a iancoleman user you shouldn't be getting invalid, most of the time it happens because of space and capital letters.
If none of these are the case then the derivation path is where you should look into just like some suggested on here, that shit can be complicated for a beginner though but if you can take your time you will get it.
I think I tried like 500 times with different parameters in the past 20 hours.
Tried my seed frase on iancoleman.io, it shows "invalid mnemonic".
Looks like its a native Etherium seed frase. That means the only option is - I used an extended seed frase? Because you cannot mess with derivation path, when creating a seed in Electrum. Or am I wrong?