Open your phone's internet browser and go to securly.com/ssl to download the certificate. It may say it is already installed - close this and click download anyway.
Open your phone Settings.
Search for or go to Security (or Privacy & Security), then look for Install from storage or Encryption & credentials.
Select CA Certificate and choose the downloaded Securly file to install it.
Open the Safari app (this won't work in Chrome) and go to securly.com/ssl.
Tap Download, then tap Allow to download the profile.
Open your iPhone Settings and tap Profile Downloaded near the top.
Tap Install, enter your passcode, and confirm.
Go back to Settings > General > About > Certificate Trust Settings.
Find the Securly certificate and turn the switch ON to fully trust it.
