Did I translate this sentence correctly?

接待交際費をけっこう使えたんだ

"I use a lot of expenses for eating and entertainment (with clients)"?

This is a businessman talking about his job.

接待 = entertainment, treating, dining
交際 = company, friendship
交際費 = entertainment expense
接待費 = entertainment expense

How come they both mean the same thing with the kanji 費 at the end? I'm confused and wondering if there's a more correct (or better) translation for this.

I would say:
- I used to be able to spend a lot of company expenses for client entertainment.
- I used to have access to a lot of company fund for client entertainment.

The reason I say “used to be able to…” (only in the past) is because it says 使えた = I could use (the expense), and it sounds like he no longer can.

接待交際費 is one general term for client entertainment expenses in corporate context.
接待費 would be taking out clients for dining & wining
交際費 might be referring to seasonal gifts you might present to the clients, etc.

Sales people who have good sales record might be allowed a bigger budget for their client entertainment, so it sounds a bit like he is boasting :)

I thought it meant
"I was allowed to use a lot of expenses for client entertainment (on that day)."

The 使えたんだ part really depends on the context. The 接待交際費 part is as AK explained. But let me just add that 交際費 could also include expenses where you split the bill with a (possible) business partner while 接待費 are the expenses that are used for treating a (possible) business partner. And to be precise, it's not always a "company" that pays these expenses. It could be an individual business person who pays the expenses, or a non-company organization, or yourself if you're self-employed.

Either way, in that sentence, it's natural to assume that the speaker was either hired by someone with enough money, or was making a lot of money himself. And he didn't have to use his pocket money to let someone have fun or even perhaps have fun with someone.

Thanks a lot for your explanation, guys! :)