user134120: The reason I ask is an online casino was set to pay me $1,000 via Bitcoin and showed me the address they claim to have paid, which is identical to mine except the very last letter is capital and on mine it's a lower case. Is it possible to create another address so similar to mine?

user208: It is not possible to have two valid Bitcoin addresses that differ only in their last 5 characters at all, as those only contain checksum data. For bech32/bech32m addresses (bc1...), that's even true for the last 6 characters.
In theory, it is possible to construct two P2PKH (1...) or P2SH (3...) addresses that differ only in 1 character if not at the very end, but the probability is very low that any given addresses has such a valid mutation (1 in ~75 million). With bech32/bech32m any two valid address differ in at least 5 characters.

134120: <p>The reason I ask is an online casino was set to pay me $1,000 via Bitcoin and showed me the address they claim to have paid, which is identical to mine except the very last letter is capital and on mine it's a lower case. Is it possible to create another address so similar to mine?</p>
 208: <p>It is not possible to have two valid Bitcoin addresses that differ only in their last 5 characters at all, as those only contain checksum data. For bech32/bech32m addresses (bc1...), that's even true for the last 6 characters.</p>
<p>In theory, it <em>is</em> possible to construct two P2PKH (1...) or P2SH (3...) addresses that differ only in 1 character if not at the very end, but the probability is very low that any given addresses has such a valid mutation (1 in ~75 million). With bech32/bech32m any two valid address differ in at least 5 characters.</p>
