is it true that one node can connect with one next-node by only one flow? (how to merge two plots?)

[christina-cqq]

I wanted to merge two sankey plots (mariculture and capture) with the same nodes (oceans) and the same next-node (country's income level), but different flow values (mariculture amount and captured amount). I was planning to use one sankey plot to show the two flow values at one time, the total values at nodes and next-nodes can be respectively added up. But it seems to be unable to do so? hence the question, is it true that one node can connect with one next-node by only one flow? In my case, I want to connect them with two flows.

library(ggplot2)
library(ggsankey)
library(dplyr)
#prepare the mariculture data, node is ocean, next_node is income level, value is seafood amount   
 dfa<-dfaqua.incomelevel %>% 
  select (node , next_node , value)%>% 
  make_long(node, next_node, value = value)  %>% 
  mutate(type = 'Mariculture') 
dfa<- data.frame(dfa)

#prepare the capture data, node is ocean, next_node is income level, value is seafood amount 
dfc<-dfcatch.incomelevel %>% 
  select (node , next_node , value)%>% 
  make_long(node, next_node, value = value)   %>% 
  mutate(type = 'Capture') 
dfc<- data.frame(dfc)

#combine the two make_long data, data are provided here https://filetransfer.io/data-package/5wKjjvvU#link
dfinput <- rbind(dfa, dfc)
dfinput <-dfinput%>%
    group_by(x, node) %>%
    mutate(total = sum(value))

#make the merged sankey plot, but the output is weird, not what I want
g  <- ggplot (dfinput
                    , aes(x = x
                    , next_x = next_x
                    , node = node
                    , next_node = next_node
                    , fill = factor(type) #only colour the flow by type: mariculture and capture
                    , value = value #flow value
                    , label = paste0(node, " (", round(total,0), ")")
))+
  geom_sankey(flow.alpha = 0.5, node.color = 1) +
  geom_sankey_label(size = 3.5, color = 1, fill = "white") +
  scale_fill_viridis_d() +
  theme_sankey(base_size = 16)+
  guides(fill = guide_legend(title = "Income Level"))
print(g)