Error message when joining two dataframes with sf -Error: y should be a data.frame; for spatial joins, use st_join

In R, I’m trying to count the number of points which fall within a buffer around polygons and add the count result to the original shapefile from which the polygon file was created. I’ve followed the answer provided by @Guzmán from this question: Counting number of points in polygon using R?. Everything works fine until it comes to adding the result to the original shapefile, which I want to do based on the attribute “ID”, i.e. not a spatial join. I get the error message “Error: y should be a data.frame; for spatial joins, use st_join” even though y is a dataframe (at least it is according to is.data.frame).

library(sf)
library(dplyr)


OrigPolys <- st_read("OrigPolys.shp") #Load polygons
Points <- st_read("Points.shp") #Load points
NewPolys <- subset(OrigPolys, X1 != 'NA') #Subset required polygons
Buffer <- st_buffer(NewPolys, 5000) #Create buffer NewPolys
inter <- st_intersection(Buffer, Points) #Find points in NewPolys
int_count <- inter %>% 
  group_by(ID) %>% 
  count() #Count number of Points in Buffer
as.data.frame(int_count) #Convert to df (not sure if this is required as is.data.frame = T whether included or not)
OrigPolys_Pts <- left_join(OrigPolys, int_count, by = "ID") #Join count to OrigPolys based on "ID" attribute```