Hey there!
There are many, many reasons why the Confederation Congress called for the constitutional convention to amend the Articles of Confederation.
1. The central government had very limited power under the Articles of Confederation. While these Articles were being written, a powerful central government was feared, so people gave the power to tax and regulate trade to this states, which caused too much unnecessary confusion, which is why amending was needed. The government also had little power to enforce laws.
2. There was no national judicial or executive branch of government, only lawmakers. This gave lots of power to one legislative branch that could not be balanced by anything else, which would lead to corruption.
3. The articles of confederation gave Congress the ability to make a military, but because Congress had little money because they could not tax, they could not raise an army. There had to be a structural change so the country could be safe.
These are the three main reasons, but there were also some problems with the states regarding representation and voice in the government.
I hope this helps!