Finding Gaps Between the dates

Create the following calculated columns

Next Invoice Start Date = 
CALCULATE(
    MIN(Invoice[Invoice Start Date]),
    FILTER(
        Invoice,
        Invoice[Account Number] = EARLIER(Invoice[Account Number]) &&
        Invoice[SiteMeterIdentifier] = EARLIER(Invoice[SiteMeterIdentifier]) &&
        Invoice[Invoice Start Date] > EARLIER(Invoice[Invoice Start Date])
    )
)

Gap Start Date = 
IF(
    ISBLANK(Invoice[Next Invoice Start Date]),
    BLANK(),
    IF(
        DATEDIFF(Invoice[Invoice End Date], Invoice[Next Invoice Start Date], DAY) > 1,
        Invoice[Invoice End Date] + 1,
        BLANK()
    )
)

Gap End Date = 
IF(
    ISBLANK(Invoice[Next Invoice Start Date]),
    BLANK(),
    IF(
        DATEDIFF(Invoice[Invoice End Date], Invoice[Next Invoice Start Date], DAY) > 1,
        Invoice[Next Invoice Start Date] - 1,
        BLANK()
    )
)