You need an embassy visa for Bulgaria if you have an Indian passport
Visa options for Bulgaria
Visitor visa
Travellers need a visa to visit Bulgaria for Business or Tourism. A paper or embassy visa is the only visa available for travellers visiting Bulgaria. The visa is typically a stamp or sticker added to the passport. Travellers must obtain this visa from a local embassy, consulate, or visa center before travelling.
This is not offered by sherpa°.
Apply on the government site.