Tax reports on Koinly are priced separately for each year and are based on the number of transactions during that year.
Upgrading a plan
You can upgrade a tax report by paying the difference between the price you already paid and the price of the new plan.
Account-wide transaction limit
There is an account-wide transaction limit that is based on the total number of transactions in your account. This limit increases every time you buy a tax report (by the maximum number of transactions allowed by the report plan). The reason we have this limit is because Koinly needs to process all past-year transactions in order to calculate your gains for a later year. However, once you purchase a tax report then this account limit is increased permanently.
Why is a plan locked even though I have fewer transactions during the year?
This is most likely due to the account-wide transaction limit. If you exceed the base account limit of 1000 transactions, you have to purchase a plan that will increase the limit to cover the total transactions in your account. You can also increase the limit by purchasing reports for previous years or purchasing a higher plan for the year you need a report for.
Example
Let's say you had 8000 transactions in 2018 but only 50 transactions in 2019.
If you only need a tax report for 2019 then you can purchase the Pro plan for this year which would increase your account limit by 10,000 transactions and thus cover all transactions in your account. Note that this plan would only give you access to the 2019 report.
If you need reports for both 2018 and 2019 then you would need to buy a Pro plan for 2018 first and then buy a smaller plan for 2019.