When mapping Matrix rooms to XMPP, certain characters are not valid in JIDs and must be escaped. The default mechanism for that is XEP-0106, which also provides a list of which characters to escape:

• U+0022 (")
• U+0026 (&)
• U+0027 (')
• U+002F (/)
• U+003A (:)
• U+003C (<)
• U+003E (>)
• U+0040 (@)

Please convert those into the respective escaped hexadecimal notation, i.e. " --> \22