The deal was that Russia would allow Ukranian grain shipments through the Black Sea. In return Russia would be able to export its grain and fertilizer as before the war. The latter meant that transactions for grain and fertilizer would have to be excluded from the sanctions on russian use of SWIFT. In short the deal would have been that both countries would be allowed to export their agrarian products without foreign sanctions. Like before the war.

Russia kept its part of the deal, Ukraine could export its grain unhindered by the russian fleet. However, Russia never received what it was promised in return by western guaranteurs (ukraines backers who cut Russia off of SWIFT). This lead to situations where russia had shipped fertilizer to the recepient country, but the monetary transaction was impossible to conlude, because Russia was still barred from SWIFT while the recepient country had not yet acess to the russian version of SWIFT. Money could not move from one account to the other, so to say.

The fertilizer thus sat in the harbor, doing nothing. In these cases, Russia turned said fertilizer into a gift to the recepient country, thus no money having to change accounts and the western sanctions backfiring with the west losing diplomatic capital, while Russia gained some. People tend to like gifts and do not like being threatened with starvation.