There are a few reasons why your subscribers might not appear in your MailChimp list, while they do show in your MailMunch account. It could be because of either of the following reasons, or a combination of these reasons.
There are required fields other than Email in your MailChimp list but no matching fields in your form on MailMunch. If this is the case then an error will be generated against your subscribers which you can access in your subscriber details. In this case, you can either mark these fields as optional in your MailChimp list, or create a new field in your MailMunch form in the Fields step and map the MailMunch form field with MailChimp list field in the Integrate step to resolve this issue.
Double opt-in is enabled. If you have double opt-in for MailChimp enabled, your subscribers will receive a confirmation email from MailChimp and will have to confirm their subscription before you see them in your MailChimp list. You will still see them in MailMunch though.
You do not have an active list selected. This is a common reason. Maybe when you integrated MailMunch with MailChimp, you did not have any list in your MailChimp account. You must have at least one list in your MailChimp account and an active list selected in your MailMunch account.
Marketing Permissions are not selected. If you have Marketing Permissions enabled in your Mailchimp account, you need to add Consent Field to your MailMunch form and check the Marketing Permissions option in the Integrate step of the form.
Note: Any subscribers you had in MailMunch before integrating with MailChimp will not be synced automatically. For old subscribers, you can export them in a CSV file, and import to MailChimp manually. Any new subscribers will automatically be added to your MailChimp list instantly.