When connecting a source in Funnel you'll get prompted to choose Report Type.
Standard here is the same as Campaign performance. Not all data is available in all report types, so make sure you're looking at the same thing when comparing data between Funnel and Google Ads. For instance, if you connected a data source with the shopping report, make sure you compare it with a shopping report in Google Ads.

If you have a problem with a conversion mismatch the most common one's we've noticed are explained here: Why can't I see all my Google Ads (AdWords) conversions?

Conversion time data is only available after March 6, 2019. Store visit conversions and store sales conversions are not included.

If you have a problem when connecting a source then a common reason could be that you've connected a Google account on the wrong "level". This is explained here: About access levels in your Google Ads Account

If you try to reconnect a source with existing credentials and it fails results in a TokenError "Invalid grant", try to reconnect adding new credentials using the the same login/email. This will replace the old faulty credentials with new ones.

If this doesn't help please reach out to our support for further advice.

Sometimes we've noticed that fields display name and id in AdWords/Google Ads is not the same. Please have a quick look here: All report reference and make sure that we don't already support your missing field but that it is called something else.

When connecting a keyword/placement level ad report in Funnel one should have in mind that keyword/placement data will cause all of the data for this source to get segmented. This means if comparing a Campaign level report (Google Ads UI) with a Keyword/placement level Ad report (Funnel), there might be differences in the totals since some data doesn't fit the segmentation of keyword/placement.
If you're seeing a mismatch between your keyword data in Funnel and in AdWords, look for a row with keyword value "Content". This row holds all your data from the display network. Filter it out and your data should match up with your search network keywords.

If the optional dimension Click Type is used for a data source be aware of that the value of impressions might get inflated because of extensions. The ad it self will get one impression and then each extension that have been shown together with the ad will also get one impression each, triggering up the total number of impressions for that ad.

If you want to see the "normal" amount of impressions with Click Type, you can try filtering impressions by Click Type. Viewing only impressions with the Click Type "URL_CLICKS" will give the expected amount of impressions in most cases.

We have also seen mismatch for cost and conversion if you select Click Type. The reason for this is at the moment unknown but Google is investigating it.

For Geo Performance report you can choose optional Geo Dimensions like "country", "region", "city" etc. When adding Geo Dimensions only rows with a value for all selected dimensions will be downloaded - i.e. you have chosen “country” and “city” as geo dimensions, only the rows that have values for both the city and the country will be downloaded. This means that you will lose all the rows that only have a country registered but no city.

Therefor you need to consider carefully what optional Geo Dimensions to choose when connecting a Geo Performance report, as rows might be dropped.

Google has chosen this behaviour in the Google Ads API to better match what is seen in the Google Ads UI.

Video Campaigns are not fully supported in Geo Performance reports.

Some geographical dimensions will show up as "geoTargetingConstants/{number}" because they cannot be translated into a familiar geographical name, i.e. country, territory, city etc. This is due to sanctions imposed by the United States Office of Foreign Assets Control and no workaround is available.

When connecting a data source with the audience report type, it is important to keep in mind at what level your audiences are applied in Google Ads, and match that report level. If for example you apply audiences at campaign level in Google Ads, your data source needs to use the report level "Campaign".

The audience type "Detailed demographics" is not supported in either of Googles Ads APIs.

Sometimes Views (100%) can be higher than video views. This might seem strange but the Views (100%) metric is based on Video played to 100% * number of video impressions. This can also happen for Views (75%/50%/25%) but is less likely.