It's been researched that every country has their adjectival form (exception is a demonym, which denotes nouns), such as the adjectival form of Mexico is Mexican, the adjectival form of Russia is Russian, and their currencies are "Mexican peso" and "Russian ruble", respectively.
In currencies, mostly I have found adjectival forms of the countries e.g. Mexican peso and Russian ruble. But what happened to the adjectival forms of Belize, Singapore, Lesotho and Turkmenistan, as their currencies are:
Belize dollar (rather than Belizean dollar)
Singapore dollar (rather than Singaporean dollar)
Lesotho loti (rather than Basotho loti)
It's been noted that the word "Basotho" is both demonym as well as the adjectival form of Lesotho. And "Basotho" as a demonym is plural per se; its singular form is "Mosotho".
- Turkmenistan manat (rather than Turkmenistani manat)
Out of 190+ countries, these countries are the exceptions which have no any adjectival forms in their currencies.
The Google Search Engine supports what I thought of those adjectival forms. See that when you type "Singaporean dollar" on Google, then it pops up that exact option, but when you search it, it doesn't show any exact result, rather it says Singapore Dollar. I wish I could know its reason.