This article tells you what to do when Solo notifies you that the month cannot be closed.
"Accounting month can not be closed because all the account transactions have not yet been received." This notification appears when Solo has not received information on the last account transactions of the month. This means that the first account transactions of the new month have not arrived from the bank yet. Solo uses this as the sign that all the transactions of the previous month must have arrived.
For example, if you use weekly bank statements, the first bank statements after the turn of the month might not arrive before the 7th day of the new month. In this case, the material cannot be submitted at the turn of the month, because Solo does not know all of the transactions at the end of the month.
The notification will disappear when Solo receives the first account transactions of the new month. The material can be submitted after this.