This error originated from a custom integration.

Logger: homeassistant.config_entries
Source: custom_components/iammeter_http/init.py:52
Integration: Iammeter_http
First occurred: 15:28:47 (1 occurrences)
Last logged: 15:28:47

Error setting up entry iammeter for iammeter_http
Traceback (most recent call last):
File "/usr/src/homeassistant/homeassistant/config_entries.py", line 383, in async_setup
result = await component.async_setup_entry(hass, self)
File "/config/custom_components/iammeter_http/init.py", line 22, in async_setup_entry
coordinator = IammeterData(hass, entry)
File "/config/custom_components/iammeter_http/init.py", line 52, in init
self.port = entry.data[CONF_PORT]
KeyError: 'port'

Error occurs on restart after upgrading from v1.0.9 to v1.0.12
I have restored back to v1.0.9 til this issue can be resolved

Running HA:
Home Assistant 2023.3.5
Supervisor 2023.03.2
Operating System 9.5
Frontend 20230309.1 - latest

Iammeter Information:

Firmware Ver.: ATVi.75.98.1@MX1290
Running Cloud Mode
Model: WEM3080T

Can the above operation solve your problem

Hi. You should log into GitHub repository for IAMMETER. There are a few issues that need your attention 

I was upgrading from v1.0.9 to v1.0.12 in the following two versions, and no errors were found

1.

Home Assistant 2023.2.5
Supervisor 2023.03.2
Operating System 9.5
Frontend： 20230202.0 - latest

2.

Home Assistant 2023.3.6
Supervisor 2023.03.2
Operating System 9.5
Frontend： 20230309.1 - latest

From your error message, it may be caused by adding a custom port in v1.0.11. After upgrading to v1.0.12, you can try to delete it in Devices&Services and add it again.