Server Name and lmgrd Port Number
Make sure that the server name in your client side license.dat and server side Maple2020.lic are the same.
The server name and lmgrd port number in the license.dat are on the line:
SERVER server_name ANY lmgrd_port_number
The server name and lmgrd port number in the Maple2020.lic file is on the line:
SERVER server_name DISK_SERIAL_NUM=aaaaaaaa lmgrd_port_number
These can be seen in the image below.
maplelmg Port Number
Make sure that the maplelmg port number is declared in the Maple2021.lic file. This port number is found on the line:
VENDOR maplelmg PORT=28010
You can change 28010 to any port that is open or can be opened on your network.
This can be seen in the image below.
Image of Sample Network License
In the image below you can see the (only) three parts of a license file that can be changed. The server name (1), the lmgrd port number (2), and the maplelmg port number (3). A license file may use a single Host ID rather than a Disk Serial Number (Volume Serial Number) but this must be determined during activation. 
Note: You must restart the server for any changes to a license file to take effect.
Open Ports on Firewall
Instructions on how to check that the ports are open can be found here. You can open ports in the Windows firewall by doing the following:
1. Search "Windows Defender Firewall with Advanced Security" from windows search
2. Click on Inbound Rules, then right click on Inbound Rules and select New Rule
3. Add the port to open and click Next.
4. Enter the protocol as TCP and the port number then click Next.
5. Select Allow the connection and hit Next again.
6. Choose the network type, hit Next and then Name the rule and hit Finish.
7. Click on Outbound rules, then right click on Outbound Rules and select New Rule and repeat steps 3-6.
Note: This will need to be done on the server and client machines. As well it will need to be done on the network and any sub-networks.
If you use another firewall you should be able to find instructions on opening ports from the vendors website.