Deeerby

That sort of error is caused by Steam unreliability. Just retry and hopefully it should work.

This is how you would encapsulate it:
const offerObject = await new Promise((resolve, reject) => tradeHandler.manager.getOffer(depositResponse.offerId, (err, offer) => { if (err) { return reject(err); } resolve(offer); });  

Accepting a specific offer by ID without retrieving its data first isn't a supported use-case for TradeOfferManager, since it's designed to make the process as simple as possible and performs various checks and such. You'd need to either fetch the offer first using getOffer or manually craft the HTTP request that TradeOfferManager makes.