In Attack of the Clones it was established that a Senator may leave the Senate and have someone else act on their behalf. We saw this when Senator Amidala left Jar Jar Binks in charge. While he then has the title of Acting Senator Binks, or more commonly Senator Binks.

In Andor we have a similar situation. When Mon greets Benjamin Bratt's character she says "Senator Organa", but this is not Bail Organa. This is in fact a brother or cousin of Bail Organa. Mon is aware that Bail Organa is currently sick (not really, he's doing some secret Rebel stuff, but that's a secret), but she still greets him as Senator Organa because that is the polite and proper thing to do.

Now, you're probably wondering, seconds after the above scene Mon's husband Perrin says, "Bail", which really seems like it must be Bail Organa.

We have two options here. The first is that when he said "Bail" he meant "Bayle". I know the subtitles report differently but it's all part of a larger scheme. Disney wants us all to think it's "Bail Organa" but it is in fact his brother/cousin "Bayle Organa". This is a trick so when they kill him next episode it will be a shock, only for the real Bail Organa to appear.

The second option, and more likely, is that Perrin is just being a dick. That fits his character. He calls him Bail as an insult. He knows he isn't Bail and is just filling in, so after Mon respectfully calls him Senator Organa, he uses the false name "Bail" to mock him.

Now keep in mind this nonsense only works if Benjamin Bratt never makes another appearance... Which he probably will next week.