Swap API request often fail (ORDER_UNFILLABLE, Return amount is not enough)

After some time I made it to sign and send Swap API requests with Python. Unfortunately I have the problem that every second transaction fails with an error (losing the high transaction fee of course…).
Since I never got failing transactions from the UI interface I guess I do something wrong with the parameters.

I only use high liquidity pairs like BUSD/BTCB. This is one request which sometimes fails:
https://api.1inch.exchange/v3.0/56/swap?fromTokenAddress=0xe9e7cea3dedca5984780bafc599bd69add087d56&toTokenAddress=0x7130d2a12b9bcbfae4f2634d864a1ee1ce3ead9c&amount=1000000000000000000000&fromAddress=XXX&slippage=0.25

Transaction which failed with “ORDER_UNFILLABLE” or “Return amount is not enough”:
0xd4efc7b38101baa96e1b5f2f605e81f3a9bd3a04768a69e0393b17c6395a0e63
0x13c3528d71872f7b5d799086fafa486a67cbe6cc734b7ade5837029ae59ac119

I sign and send those transaction as is. I don’t change the estimated gas of the transaction or anything. I don’t wait, I send them immediately.

Do you have any tips for my API calls which could reduce the likelyness of failing?

Ok, I found out it’s most likely the slippage which creates these problems. However increasing the slippage to 5% or something to be “safe” is no option for me since I can’t accept that.

The problem is the chosen protocol of the swap often times I guess. There is often PANCAKESWAP (V1) or something with low liquidity included which seems to give good returns but is bad to execute due to high slippage. Any advices here? The API doesn’t allow white/black listing like in the UI.