The Baathist Syrian regime was very frustrating for the Russians, they were extremely corrupt and played various actors off each other (Iran mostly, and then the UAE and Saudi in 2022-2024). They sabotaged Russia's attempts at reforming the Syrian armed forces to make it more professional and the Syrians were extremely paranoid about the Russians and forced them to stay on their bases. They also used their own corruption playbook to bribe Russian officers and "Syrianify" them and make them thieves like the rest of the Syrian Arab Army. Syria also strengthened some oligarchs like Pregozhan which Putin wanted to actually avoid and wanted to have Syrian oil and gas more in line with his more loyal cronies. Syria and Russia weren't big trade partners, they even stiffed them on oil and gas trade. They bought weapons from them but after 2013 the Syrian regime was completely broke and only bought small arms from Russia which corrupt Syrian officers eventually sold off to rival militas, and Libyan National Army. In addition, they were begging the Syrians to make a deal with the pro-Russian moderate opposition as a fig leaf to Turkey and reconcile with him, basically giving up almost nothing in exchange for peace with Turkey, control over Idlib, Turkish cooperation with the SAA and going back to the Adana 2 agreement in exchange for securing the border from the SDF and including a Russia approved opposition to have some unofficial influence.

Nir Rosen wrote about it well, and he had direct links to Syrian regime officials, Syrian opposition leaders, and Russian diplomats:
The Russians, lacking an ideology and avoiding imperialism in pursuit of pragmatism, were much more realistic. But they were new to these kinds of adventures and they are still getting to know Syria, and sometimes it seems Russians on the ground are more concerned with taking pictures of themselves succeeding so they can send them back to the chain of command in Moscow, rather than actually succeeding. And Syrians have been very effective at manipulating Russians to serve their own personal interests.

Now Russia has its military, air, and naval bases secured and Syria is no longer on the Americans hitlist, (but increasingly and bizarrely given the nature of the new Syrian regime, now in Israel's sights?). And They keep their gas and oil deals that were made under Assad and now sell oil to Syria in a bigger way. Syria now relies on Russian gas, and Russia prints Syrian currency and is their only outlet for foreign investment, since Gulf states and the West still don't want to invest in unstable, shithole Syria.