An FAQ about importing data into Firefly III
Firefly III has many tools to import transactions. You must install these tools separately.
Most tools come with the necessary hooks to automate the import yourself. This also depends on your bank's support for these kinds of things.
The Spectre API is a paid product by Salt Edge. It's used by many financial tools, fintechs and others in the financial space. They are kind enough to offer trials to users of Firefly III, but these are limited in time and scope. Salt Edge is a business-to-business organisation, which is reflected in their pricing: the cost of their API starts at about 500$ per month.