The easiest way is to spend the outbound liquidity on something, moving it to inbound.

Can I just send some sats to SN to prevent these types of errors?

Yep. I often rebalance by zapping like mad some days, or by paying our dev bounties from my node, or buying cowboy credits for @sn.

If you use an exchange or a custodial wallet that uses lightning you can also just send sats to yourself from your node (self-custodial lightning has awesome sender privacy).

Another option is to loop out with something like loop or boltz and pay a lightning invoice that gives you the bitcoin back to an onchain address you specify.